1. Field of the Invention
This invention relates to test sets for testing vision with analog progressively selected lens settings for determining precise requirements for prescription eyeglasses and for determining viability of a patient's retina, and in particular, to a method and apparatus for measuring requirements for lenses for aiding low vision which has been impaired by macular degeneration, optic nerve damage or similar low-vision problems.
2. Description of the Prior Art
Two main types of test sets for measuring visual acuity have been devised previously and are generally referred to as a surface-mounted or floor-stand type and a test-eyeglass type. Both use incrementally stepped gradations of lens types and corrections that are put into them for testing a person's vision. The more common surface-mounted type has a lens-holder arrangement which can be suspended in front of a patient and includes a plurality of lenses which can be positioned for the patient's use. The patient views a chart through various ones of the lenses, selecting the one which provides the best visual acuity.
The main problem with both of these prior types of lens test sets is that they do not provide for vision testing with continuous variation of lens characteristics. Instead, they provide testing with only stepped variation of lenses. The stepped variation of lens characteristics may miss the optimum selection of dioptric values. Furthermore, these prior art systems may not focus an image on the more optically responsive surfaces of the macular retinal membrane.
Young and healthy eyes generally can adjust to errors and inadequacies resulting from stepped variations in lens selections and from improper focusing. However, when faulty vision is caused either by the degeneration of the whole or a part of the macular retinal membrane on the back of the interior face of the eyeball, or by deterioration of the optic nerves which would normally carry the images from the macular retinal membrane to the brain, more accurate methods than the stepped gradation of lenses is required. The extent of error in focusing and the extent of variation of gradation of test lenses can be so great that the entire vision capacity of a low-vision patient may be missed or distorted with present testing methods.
In some cases, direction of additional light into the eye may be required to achieve even minor vision. Present testing methods do not provide means for testing the effects of reflecting additional light into select portions of the eye nor for testing to determine which parts of the eye may be aided by the reflection of additional light.
The present floor-stand test sets do not provide opportunity to test the effects of changes in incline of the body and the effects of normal light conditions with the test lenses. For patients with low vision, this can be crucial.
Furthermore, present test sets are not believed adequate for identifying viable retina areas in patients suffering from heavy cataracts. It is desirable to be able to identify light responsive retinas in such patients prior to undergoing surgery.
Although the conventional test-eyeglasses method of assessing the effects of lenses with stepped gradations can be employed in normal wearing conditions, the stepped error factor is as great as for the floor-stand type. Moreover, it is very time consuming for both doctor and patient and, therefore, expensive and often psychologically prohibitive. Still further, neither of the present systems provides for relative movement of separate lenses in order to identify the most optically responsive area of eyes with macular degeneration.